Actual printed size differs from design

  • I've had my printer for about a year (Ender 3) and have used Matter Control for about the last 9 months. I haven't done a lot of printing and what I did print didn't require much dimensional accuracy (I'm using PLA). Recently, the last few projects have been smaller, by about 10% when printed, than what the measuring tool indicated. I opened an .stl file for a fan grill (120mm) that had 105mm hole spacing for the mounting holes, and I confirmed the dimensions were correct before printing. The holes ended up at about 103mm when printed. Another project had recesses for 4mm nuts, and again, it was to small. I printed a second one but I increased the scale by 10% and the 4mm nuts dropped right in, a perfect fit. I understand that some of this difference is due to shrinkage but I can't believe that it would be as much as 10%. Can anyone suggest a good strategy for improving the dimensional accuracy of my prints? Adjustments to the printer or within Matter Control? Or, upscale everything I print by a certain percentage? I would appreciate any suggestion you may have to offer.

  • May have to take a look at the wall thickness settings. It could be that, for example, the setting for making "thin walls" thicker could be causing the slight change in size. Simple settings like that can make a difference.

  • MatterHackers

    10% is VERY high. Holes are pretty much always undersized - it's basically inherent to the process of FDM printing. Typically, though, it's a static amount. For example, my main printer typically undersizes holes by 0.20mm. So if I need an 8mm hole, I size it to 8.2mm. If I need 20mm, then 20.2mm.

    Over-extrusion could be the cause for some of what you're seeing, so I'd recommend confirming your extruder is properly calibration.

    Also, printing perimeters outside > in instead of inside > out can also improve dimensional accuracy - though you may have more prominent Z-seams.

    Keep in mind that PLA can shrink as much as 3% (typically 0.5-1.5%) so that's going to factor in as well - and could completely explain your 105mm - 103mm holes.

  • Global Moderator

    Ive seen this happen frequently. It has nothing to do with MatterControl. I post my designs on the Prusa community page and my designs come out 10% smaller than normal for them. STL files contain no scale information, and the units are arbitrary. I don't know if there is a fix for this. I think it is best to check your measurements before you print someone else's STL.

  • @tinken Interesting. Thats good to know. Thank you tinken.

  • PLA is known for high shrinkage, on average you get about 1.6%
    So i now always use PLA Pluss and now only get about 0.2 -0.3% shrinkage
    Remember different brands either have better or bad quality PLA
    I use Esun PLA+ which has very good properties and strong, I have tried Tronxy and I have found it bad & unusable for my models
    Maybe some one could start a post on filaments that work best for there printers and models.

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